Viscoelastic dentifrice composition

ABSTRACT

A toothpaste or dental gel composition containing an amount of a synthetic linearly viscoelastic cross-linked polymeric thickening agent, especially a cross-linked methyl vinyl ether/maleic anhydride copolymer, effective to render the composition linearly viscoelastic, and a method of promoting oral hygiene by applying an effective amount of the composition to dental surface.

This is a division of application Ser. No. 07/738,766 filed Aug. 1, 1991now U.S. Pat. No. 5,202,112.

This invention relates to novel dentifrice compositions, especially totoothpastes and dental gels having viscoelastic properties.

A thickening agent (binding or gelling agent) is commonly employed indentifrice compositions to prevent separation of ingredients in storage,promote dispensability and retention in use as on a toothbrush, improvecosmetic properties and the like. Such thickeners are generallyhydrophilic colloids which disperse in aqueous media. The most widelyused thickeners are cellulose derivatives because they are cheap andtheir quality can be closely controlled. Sodium carboxymethyl cellulose(NaCMC) is the most widely used thickener in dentifrices but suchthickened dentifrices are often subject to syneresis, i.e. severe lossof rigidity and viscosity. It is believed that this may be caused partlyby enzymatic degradation of the NaCMC by cellulytic enzyme (cellulase)which can be produced by moulds and bacteria present in some batches ofNaCMC. These microorganisms may originate in the water, or on storage ofthe NaCMC, in damp conditions which support growth, or from othersources of contamination. Killing the organism responsible does not, ofcourse, remove the enzyme already produced.

Hydroxyethyl cellulose is a thickener with a better resistance tocellulytic attack than NaCMC, possibly due to its more uniformsubstitution pattern along the molecule compared with NaCMC, but indentifrice formulations, it often produces a product with anunacceptably "long" or "stringy" texture.

U.S. Pat. No. 4,254,101 to Denny proposes the use of carboxyvinylpolymers as thickeners in toothpastes containing silica abrasivepolishing materials and high levels of humectant materials to provide"excellent texture" and improved fluoride ion availability to dentalenamel. The carboxyvinyl polymers are disclosed as colloidally watersoluble polymers of acrylic acid crosslinked with about 0.75% to 2.0% ofpolyallyl sucrose or polyallylpentaethrythritol, obtainable under theCarbopol trademark from B. F. Goodrich. It is known, however, thatCarbopol is hard to disperse. B. F. Goodrich suggests the use of aneductor and other specialized procedures to get good dispersions. Theproblem arises because Carbopol is so hydrophilic that the individualparticles swell and the particles clump to form aggregates. Whendispersion is attempted, the outside of the aggregate hydrates andswells. The inside is no longer readily contacted with water. Thiscauses fish eyes and regions of inhomogeneity that are very hard toremove by further mixing. The fish eyes and inhomogeous dispersionpersist in the final product. The result is decreased control over thefinal rheological properties of the product and increased batch to batchvariation. These variations are readily perceived by the end user andare interpreted as poor quality product.

It is an object of this invention to provide dentifrice compositionswhich will not be subject to the aforementioned deficiencies. Anotherobject of this invention is the provision of a linear viscoelasticdentifrice composition. Still another object of this invention is theprovision of a linear viscoelastic dentifrice composition havingexcellent stability against phase separation or syneresis, viscositychange in storage, and settling of dissolved, dispersed or suspendedparticles under high and low temperature conditions, freedom from fisheyes, excellent texture and other cosmetic properties, ease of extrusionfrom a dispensing tube, pump or the like (easily shear thinned), goodstand-up after extrusion (quick recovery of structure), and improvedfluoride ion availability to dental enamel leading to improvedanti-caries effects. A further object of this invention is the provisionof a method for promoting oral hygiene by applying to dental surface,including teeth, preferably in the oral cavity an effective amount ofthe compositions of this invention. Other objects and advantages willappear as the description proceeds.

In accordance with certain of its aspects the attainment of the objectsof this invention is realized by the provision of a linear viscoelasticdentifrice composition in the form of a toothpaste or dental gel with apH of about 4 to about 9 comprising an orally acceptable water/humectantvehicle, an orally acceptable dental polishing agent and, in an amounteffective to render the composition linearly viscoelastic, a syntheticlinearly viscoelastic cross-linked polymeric thickening agent having ina 1 wt. % aqueous solution an elastic or storage modulus G' and aviscous or loss modulus G" substantially independent of frequency in anapplied frequency range of 0.1 to 100 radians/sec, a G' minimum value of1,000 dynes/sq.cm which varies less than 1 order of magnitude of itsoriginal value, and a ratio of G"/G' ranging from more than 0.05 to lessthan 1.

The linear viscoelastic aqueous dentifrice compositions of thisinvention will, at least in the preferred embodiments, satisfy each ofthe following stability criteria over the aging temperature-timeschedule shown by the following Table A:

                  TABLE A                                                         ______________________________________                                        Aging Temperature (°F.)                                                                 Minimum Duration (Weeks)                                     ______________________________________                                        120                9                                                          100              >12                                                           77              >52                                                          ______________________________________                                    

More specifically, the compositions are considered stable if each of thefollowing stability criteria is satisfied for at least the minimumnumber of weeks for each aging temperature shown in Table I:

a. no significant visible phase separation (i.e. no solid/liquidseparation)

b. no significant change in viscosities, yield stress or otherdynamic-mechanical properties,

c. no discolorization or significant color change.

As used herein, "linear viscoelastic" means that the elastic (storage)modulus (G') and the viscous (loss) modulus (G") of the dentifrice areboth substantially independent of strain, at least in an applied strainrange of from 0.1%-10%. Dynamic oscillatory measurements are performedusing the Rheometrics System Four instrument. In this experiment anoscillatory shear field is imposed on the material, and thecorresponding shear stress response is measured. The stress is definedby a component in phase with the displacement (elastic modulus, G') anda component 90° out of phase (loss modulus, G"). The value of G'indicates the degree of elasticity and network formation in the system;see

1. Menjivar, J. A., "Water Soluble Polymers; Beauty with Performance";Glass, J. E., Ed; Advances in Chemistry 213; American Chemical Society,Washington, D.C. 1986, pp 209-226; and

2. Sinton, S.; Maerker, J.; J. Rheol. (N.Y.) 1986 30, 77, bothincorporated herein by reference.

More specifically, a dentifrice composition is considered to be linearviscoelastic for purposes of this invention, if over the strain range of0.1% -50% the elastic modulus G' has a minimum value of 1000dynes/sq.cm., and varies less then about 1 order of magnitude of itsoriginal value. Preferably, the minimum value of G' and maximumvariation of G' applies over the strain range of 0.1% to 50%.

As a further characteristic of the preferred linear viscoelasticdentifrice compositions the ratio of G"/G' (Tan δ) is less than 1,preferably less than 0.8, but more than 0.05, preferably more than 0.2,at least over the strain range of 0.1% to 50%. It should be noted inthis regard that % strain is shear strain×100%.

With respect to 1 wt. % aqueous solutions of the required cross-linkedpolymer, elastic moduli G' substantially independent of frequency andhigher than the corresponding loss moduli G" indicate solid-likebehavior characteristic of gel structure: see

3. Prud'homme, R. K.; Constien, V., and Knoll, S.; "Polymers in AqueousMedia"; Glass, J. E., Ed; Advances In Chemistry 223; American ChemicalSociety, Washington, D. C., 1989, pp. 89-112, also incorporated hereinby reference.

In such solutions, more specifically, G' and G" are substantiallyindependent of frequency in an applied frequency range of 0.1 to 100radians/sec, G' has a minimum value of 1,000 dynes/sq.cm. which variesless than 1 order of magnitude of its original value, and the ratioG"/G' ranges from more than 0.05 to less than 1.

By way of further explanation, the elastic (storage) modulus G' is ameasure of the energy stored and retrieved when a strain is applied tothe composition, while viscous (loss) modulus G" is a measure of theamount of energy dissipated as heat when strain is applied. Therefore, avalue of Tan δ corresponding to:

    0.05<Tan δ<1,

preferably

    0.2<Tan δ<0.8

means that the compositions will retain sufficient energy when a stressor strain is applied, at least over the extent expected to beencountered for products of this type, for example, when squeezed out ofa toothpaste tube or pump to return to its previous condition andexhibit excellent stand-up when the stress or strain is removed. Thecompositions with Tanδ values in these ranges, therefore, will also havea high cohesive property, namely, when a shear or strain is applied to aportion of the compositions to cause it to flow, the surroundingportions will follow. As a result of this cohesiveness of the linearviscoelastic characteristic, the compositions will readily flowuniformly and homogeneously from a pump or tube when it is squeezedthereby contributing to the stand-up and ease of extrusion propertieswhich characterize the compositions of this invention. The linearviscoelastic property also contributes to improved physical stabilityagainst phase separation of suspended particles by providing aresistance to movement of the particles due to the strain exerted by aparticle on the surrounding fluid medium.

From another aspect, a desirable rheological property which thecross-linked polymers employed herein display in solution whichindicates gel network formation is the presence of a yield point. Yieldpoint is defined as the amount of shear stresses needed to initiateflow; see

4. Goodwin, J. W., "Solid/Liquid Dispersions"; Tadros, Th. F., Ed;Academic Press, N.Y., 1987, pp 199-224, also incorporated herein byreference. At shear stress values lower than the yield point, no flowoccurs. This plastic rheology is desirable because when the gel displaysa sufficiently high yield value it allows permanent suspensions ofparticles that are formulated in the gel. This is especially importantin dentifrices, where suspension of abrasive particles is necessary. see

5. Lockhead, R. Y., Davidson, J. A., and Thomas, G.M.; "Polymers inAqueous Media: Performance Through Association"; Glass, J. E., Ed;Advances in Chemistry 223; American Chemical Society, Washington, D.C.,1989, pp 113-147, also incorporated herein by reference.

The above-described linear viscoelastic properties of the dentifricecompositions of this invention are fundamentally provided by the definedsynthetic linearly viscoelastic cross-linked polymeric thickening agentswhich generally have a molecular weight (M.W.) of about 1,000 to about5,000,000. The homopolymers and copolymers (from 2, 3 or more monomers)to be cross-linked are generally anionic comprising a chain or backbonecontaining repeating units each preferably containing at least onecarbon atom (typically only carbon atoms in the chain or backbone) andpreferably at least one directly or indirectly pendant monovalent acidicgroup, e.g. sulfonic, phosphinic, or preferably phosphonic orcarboxylic, or salt thereof, e.g. alkali metal or ammonium. It isordinarily desirable that the repeating units constitute at least about10%, preferably at least about 50%, more preferably at least about 80%up to 95% or 100% by weight of the polymer. Preferably, about 0.02 toabout 5%, more preferably about 0.1 to about 2.5% of the cross-linkedpolymer is employed in the dentifrice compositions herein.

According to a preferred embodiment, the required crosslinked polymer isderived from a synthetic anionic polymeric polycarboxylate, many typesof which are disclosed in the prior art, for example, as anticalculusagents in U.S. Pat. No. 3,429,963 to Shedlovsky; U.S. Pat. No. 4,152,420to Gaffar; U.S. Pat. No. 3,956,480 to Dichter et al; U.S. Pat. No.4,138,477 to Gaffar; and U.S. Pat. No. 4,183,914 to Gaffar et al.

These synthetic anionic polymeric polycarboxylates are often per seemployed in the form of their free acids or preferably partially or morepreferably fully neutralized water soluble or water swellable(hydratable, gel/forming) alkali metal (e.g. potassium and preferablysodium) or ammonium salts. Preferred are 1:4 to 4:1 copolymers of maleicanhydride or acid with another polymerizable ethylenically unsaturatedmonomer, preferably methyl vinyl ether/maleic anhydride (MVE/MA) havinga molecular weight (M.W.) of about 30,000 to about 1,000,000. Thesecopolymers are available, for example, as Gantrez e.g. AN 139 (M.W.500,000), AN 119 (M.W. 250,000); and S-97 Pharmaceutical Grade (M.W.70,000), of GAF Corporation. Also useful are terpolymers such as 1.0MA/0.4 MVE/0.1 dodecane, 1.0 MA/0.75MVE/0.25 decene, 1.0 MA/0.95MVE/0.05eicosene or tetradecene, 1.0 MA/0.9MVE/0.1 tetradecene, 1 MA/0.9MVE/0.1acrylic acid, vinylpyrrolidone or isobutane.

Other operative polymeric polycarboxylates include those disclosed inU.S. Pat. No. 3,956,480 referred to above, such as the 1:1 copolymers ofmaleic anhydride with ethyl acrylate, hydroxyethyl methacrylate,N-vinyl-2-pyrollidone, or ethylene, the latter being available, forexample, as Monsanto EMA No. 1103, M.W. 10,000 and EMA Grade 61, and 1:1copolymers of acrylic acid with methyl or hydroxyethyl methacrylate,methyl or ethyl acrylate, isobutyl vinyl ether or N-vinyl-2-pyrollidone.

Additional operative polymeric polycarboxylates disclosed in abovereferred to U.S. Pat. Nos. 4,138,477 and 4,183,914, include copolymersof maleic anhydride with styrene, isobutylene or ethyl vinyl ether,polyacrylic, polyitaconic and polymaleic acids, and sulfoacrylicoligomers of M.W. as low as 1,000, available as Uniroyal ND-2.

Suitable generally are polymerized olefinically or ethylenicallyunsaturated carboxylic acids containing an activated carbon-to-carbonolefinic double bond and at least one carboxyl group, that is, an acidcontaining an olefinic double bond which readily functions inpolymerization because of its presence in the monomer molecule either inthe alpha-beta position with respect to a carboxyl group or as part of aterminal methylene grouping. Illustrative of such acids are acrylic,methacrylic, ethacrylic, alpha-chloroacrylic, crotonic, beta-acryloxypropionic, sorbic, alpha-chlorosorbic, cinnamic, beta-styrylacrylic,muconic, itaconic, citraconic, mesaconic, glutaconic, aconitic,alpha-phenylacrylic, 2-benzyl acrylic, 2-cyclohexylacrylic, angelic,umbellic, fumaric, maleic acids and anhydrides. Other different olefinicmonomers copolymerizable with such carboxylic monomers includevinylacetate, vinyl chloride, dimethyl maleate and the like. Copolymersordinarily contain sufficient carboxylic salt groups forwater-solubility.

The synthetic anionic polymeric polycarboxylate component is most oftena hydrocarbon with optional halogen and O-containing substituents andlinkages as present in, for example, ester, ether and OH groups.

According to another preferred embodiment of this invention, therequired cross-linked polymer is derived from a polymer containingrepeating units in which one or more phosphonic acid groups are bondedto one or more carbon atoms in the polymer chain. Examples of suchpolymers are poly (vinyl phosphonic acid) containing units of theformula: ##STR1## a copolymer having units of vinyl phosphonic acid offormula I alternating or in random association with units of vinylphosphonyl fluoride, poly(1-phosphonopropene) with units of the formula:##STR2## poly (beta styrene phosphonic acid) containing units of theformula: ##STR3## wherein Ph is phenyl, a copolymer of beta styrenephosphonic acid with vinyl phosphonic acid having the units of formulaIII alternating or in random association with units of Formula I aboveand poly (alpha styrene phosphonic acid) containing units of theformula: ##STR4##

These styrene phosphonic acid polymers and their copolymers with otherinert ethylenically unsaturated monomers generally have molecularweights in the range of about 2,000 to about 30,000, preferably about2,500 to about 10,000. Such "inert" monomers are those which do notsignificantly interfere with the intended function of the cross-linkedpolymer.

Other phosphonic-containing polymers include, for example, phosphonatedethylene having units of the formula.

    --[CH.sub.2).sub.14 CHPO.sub.3 H.sub.2 ].sub.n --          V

where n may, for example, be an integer or have a value giving thepolymer a molecular weight of about 3,000; sodium poly (1,2butene-4,4-diphosphonate) having units of the formula: ##STR5## poly(allyl bis (phosphonoethyl amine) having units of the formula: ##STR6##Still other phosphonated polymers include, for example, poly (allylphosphono acetate), phosphonated polymethacrylate, etc. and the geminaldiphosphonate polymers disclosed in EP Publication 0321233.

As illustrative of polymers containing phosphinic acid and/or sulfonicacid groups, there may be mentioned polymers and copolymers containingunits or moieties derived from the polymerization of vinyl or allylphosphinic and/or sulfonic acids. Mixtures of these monomers may beemployed, and copolymers thereof with one or more inert polymerizableethylenically unsaturated monomers such as those described above withrespect to the operative synthetic anionic polymeric polycarboxylates.As will be noted, in these and other cross-linkable polymers for useherein, usually only one acidic group is bonded to any given carbon orother atom in the polymer backbone or branch thereon. Polysiloxanescontaining or modified to contain pendant acidic groups may also beemployed herein. Also effective are ionomers containing or modified tocontain acidic groups. Ionomers are described on Pages 546-573 of theKirk-Othmer Encyclopedia of Chemical Technology, third edition,Supplement volume, John Wiley and Sons, Inc. copyright 1984, whichdescription is incorporated herein by reference. Also effective,provided they contain or are modified to contain acidic groups, arepolyesters, polyurethanes and synthetic and natural polyamides includingproteins and proteinaceous materials such as collagen, poly (arginine)and other polymerized amino acids.

The cross-linkable polymers and copolymers described above can containmoieties in the chain or backbone derived from polymerizableethylenically unsaturated monomers in addition to and different from thedescribed acidic group-containing monomeric moieties. Polymerization isconducted in known manner, often in the presence of an initiator, andpreferably by slurry polymerization in a solvent medium in which themonomers but not the polymer products are soluble or readilydispersible.

For purposes of this invention, the above-described polymers must becross-linked to be linearly viscoelastic. The polymers are lightlycross-linked so that they swell and form gels, strong three-dimensionalnetworks in aqueous systems. Excessive cross-linking leading leading tohard, irreversible polymers is to be avoided. The amount ofcross-linking agent can vary from about 0.01 to about 30 wt. % of thetotal, cross-linked polymer, preferably about 2 to about 20 wt. %, morepreferably about 3 to about 15 wt. %.

According to a preferred embodiment, cross-linking is carried outconcurrently during polymerization of the monomeric components of thepolymer by including therein the requisite amount of cross-linkingagent. In this embodiment, the cross-linking agents are typicallyhydrocarbons of at least 4, preferably at least 5, up to about 30,carbon atoms containing 2, less preferably 3 or more, polymerizableactivated ethylenically unsaturated groups preferably in non-conjugated,terminal relationship. They can contain optional halogen and/oroxygen-containing substituents and linkages such as ester, ether and OHgroups. Examples of such cross-linking agents include 1,7-octadiene,1,9-decadiene, 1,5-hexadiene, divinyl glycol, butanediol divinyl ether,N,N'-methylenebisacrylamide, polyethylene glycol diacrylates anddimethacrylates which in each case are derived from polyethylene glycolwith a molecular weight of 126 to 8500, trimethylolpropane triacrylateand trimethacrylate, ethylene glycol, propylene glycol, butanediol,hexanediol and dodecanediol diacrylates and dimethacrylates, thediacrylates and dimethacrylates of block copolymers derived fromethylene oxide and propylene oxide, multivalent alcohols (e.g. glycerol,sucrose or pentaerythritol) di- or triesterified with acrylic acid ormethacrylic acid, triallylamine, tetraallylethylenediamine,divinylbenzene, diallyl phthalate, polyethylene glycol divinyl ether,trimethylolpropane diallyl ether, polyallyl sucrose and pentaerythritol,and divinylethylene urea and mixtures thereof.

According to another embodiment, cross-linking can be achieved after thecross-linkable polymer is formed (postpolymerization) by reaction withamounts of polyfunctional cross-linking agents reactive withcorresponding amounts of pendant reactive groups along the polymerchain, e.g. OH, NH₂, CONH₂ and especially the aforementioned acidic(e.g. carboxylic, phosphonic, phosphinic, sulfonic, etc.) groups in thepolymer. Cross-linking agents reactive with the acidic groups usuallycontain at least about 4 up to about 30 carbon atoms and may include,for example, linear and cyclic polyols such as butane and octadecanediols, polyethylene glycol, glycerol, sucrose and pentaerythritol, andthe corresponding polythiols and polyamines such as hexamethylene andoctadecane diamines and the like. Cross-linking agents reactive withother of the aforesaid pendant reactive groups include the correspondingpolyfunctional acidic compounds, e.g. containing at least 2 of theforesaid acidic groups such as butane, decane and octadecanedicarboxylic acids. Post-polymerization is usually less preferred sincethe resulting cross-linked products often tend to be more easily subjectto hydrolysis or the like with resulting loss of the desired linearlyviscoelastic properties.

It will be understood that for post-polymerization cross-linking ofmaleic anhydride-containing polymers and copolymers, the anhydride ringmust first be opened by hydrolysis to release the free --COOH groupsneeded for reaction with the cross-linking agent.

The water/humectant vehicle in the dentifrice compositions of thisinvention usually comprises about 6 to about 50% of water and about 20to about 70% of humectant (or mixture thereof) by weight of thedentifrice composition. The humectants content preferably ranges fromabout 25 to about 60% on a pure basis and the water content preferablyranges from about 15 to about 30%. The humectants/water ratio preferablyranges from about 1/1 to about 4/1.

Non-toxic, orally acceptable humectants suitable for use in thesedentifrice compositions include, for example, sorbitol (usually in theform of a 70% aqueous solution), glycerine, propylene glycol, xylitol,polypropylene glycol and/or polyethylene glycol (e.g. 400-600),especially mixtures of glycerine and sorbitol. In clear gels where therefractive index is an important consideration, a mixture of about 0 toabout 80% of glycerine and about 20 to about 80% of sorbitol with about3 to about 30% of water is preferably employed.

The present dentifrice compositions also contain an orally or dentallyacceptable abrasive or polishing material for use in conjunction with abrushing of the teeth. Examples of such polishing materials arewater-insoluble sodium metaphosphate, potassium metaphosphate,tricalcium phosphate, dihydrated calcium phosphate, anhydrous dicalciumphosphate, calcium pyrophosphate, magnesium orthophosphate, trimagnesiumphosphate, calcium carbonate, aluminum silicate, zirconium silicate,silica, bentonite, and mixtures thereof. Other suitable polishingmaterials include the particulate thermosetting resins described in U.S.Pat. No. 4,070,510 of Dec. 15, 1962 such as melamine-, phenolic-, andurea-formaldehydes, and cross-linked polyepoxides and polyesters.Preferred polishing materials include crystalline silica having particlesizes of up to about 5 microns, a mean particle size of up to about 1.1microns, and a surface area of up to about 50,000 cm.² /gm., silica gelor colloidal silica, and complex amorphous alkali metal aluminosilicate.

A silica polishing agent is preferred for use herein. Especiallypreferred are the colloidal silicas such as those sold under the Zeodenttrademark, e.g. Zeodent 113, or under the trademark SYLOID as Syloid 72and Syloid 74 or under the trademark SANTOCEL as Santocel 100 and alkalimetal aluminosilicate complexes. These polishing agents are particularlyuseful, since they have refractive indices close to the refractiveindices of gelling agent-liquid (including water and/or humectant)systems commonly used in dentifrices.

Many of the so-called "water-insoluble" polishing materials are anionicin character and also include small amounts of soluble material. Thus,insoluble sodium metaphosphate may be formed in any suitable manner asillustrated by Thorpe's Dictionary of Applied Chemistry, volume 9, 4thEdition, pp. 510-511. The forms of insoluble sodium metaphosphate knownas Madrell's salt and Kurrol's salt are further examples of suitablematerials. These metaphosphate salts exhibit only a minute solubility inwater, and therefore are commonly referred to as insolublemetaphosphates (IMP). There is present therein a minor amount of solublephosphate material as impurities, usually a few percent such as up to 4%by weight. The amount of soluble phosphate material, which is believedto include a soluble sodium trimetaphosphate in the case of insolublemetaphosphate, may and is preferably reduced or eliminated by washingwith water if desired. The insoluble alkali metal metaphosphate istypically employed in powder form of a particle size such that no morethan about 1% of the material is larger than about 37 microns.

The polishing material is generally present in amounts ranging fromabout 5 to about 70%, preferably about 10 to about 40%, more preferablyabout 10 to about 30%.

A desirable optional component of the dentifrice compositions of thisinvention is an effective amount of fluoride ions which are well knownin the art for inhibiting, preventing or eliminating caries.Fluoride-providing sources generally include compounds which may beslightly or fully soluble in water and the dentifrice compositions inthe small amounts needed or permitted to be effective. They arecharacterized by their ability to release fluoride (orfluoride-containing) ions in water and by freedom from undesiredreaction with other components of the oral preparation. Among thesematerials are inorganic fluoride salts, such as soluble alkali metal andalkaline earth metal salts, for example, sodium fluoride, potassiumfluoride, ammonium fluoride, calcium fluoride, a copper fluoride such ascuprous fluoride, zinc fluoride, barium flouride, sodium fluorsilicate,ammonium fluorosilicate, sodium fluorozirconate, sodiummonofluoro-phosphate, aluminum mono-and di-fluorophosphate, andfluorinated sodium calcium pyrophosphate. Alkali metal and tinfluorides, such as sodium and stannous fluorides, sodiummonofluorophosphate (MFP) and mixtures thereof, are preferred.

The amount of fluorine-providing compound is dependent to some extentupon the type of compound, its solubility, and the type of oralpreparation, but it must be a nontoxic amount, generally about 0.005 toabout 3.0% in the preparation. In a dentifrice preparation, e.g. gel,cream, toothpaste, an amount of such compound which releases about 25 toabout 5,000 ppm of F ion suitable minimum amount of such compound may beused, but is preferable to employ sufficient compound to release about300 to about 2,000 ppm, more preferably about 800 to about 1,500 ppm offluoride ion. Typically, in the cases of alkali metal fluorides andstannous fluoride, this component is present in an amount up to about 2%by weight, based on the weight of the preparation, and preferably in therange of about 0.05% to 1%. In the case of sodium monofluorophosphate,the compound may be present in an amount of about 0.1-3%, more typicallyabout 0.76%.

It will be understood that other conventional thickeners (binding,gelling agents) may be included in these dentifrice compositions,usually in amounts ranging from about 0.1 to about 4 parts per part byweight of the defined cross-linked polymeric thickener. Examples of suchother thickeners include xanthan gum, hydroxyethyl cellulose andwater-soluble salts of cellulose ethers such as sodium carboxymethylcellulose and sodium carboxymethyl hydroxyethyl cellulose. Natural gumssuch as carrageenan (Irish moss, Viscarin), gum karaya, gum arabic, andgum tragacanth can also be used. Colloidal magnesium aluminum silicate,Veegum or finely divided silica can be used as part of the thickeningagent system. Preferred thickening agents include xanthan gum,carrageenan, sodium carboxymethyl cellulose, sodium carboxymethylhydroxyethyl cellulose and hydroxyethyl cellulose, preferably inproportions of about 0.4 to about 3 parts per part of the cross-linkedpolymeric thickner. Also useful is synthetic hecterite, a syntheticcolloidal magnesium alkali metal silicate complex clay available forexample as Laponite (e.g. CP, SP 2002, D) marketed by Laporte IndustriesLimited. Laponite D analysis shows, approximately by weight, 58.00%SiO₂, 25.40% MgO, 3.05% Na₂ O, 0.98% Li₂ O, and some water and tracemetals. Its true specific gravity is 2.53 and it has an apparent bulkdensity (g./ml. at 8% moisture) of 1.0.

Other suitable thickners include starch, polyvinylpyrrolidone,hydroxybutyl methyl cellulose, hydroxypropyl methyl cellulose,alginates, gum ghatti, locust bean gum, pectens, and tamarind gum andthe like.

It will be understood that, as is conventional, the oral preparationsare to be sold or otherwise distributed in suitable labelled packages.Thus toothpaste, cream or gel will usually be in a collapsible tube,typically aluminum, lined lead or plastic, or other squeeze, pump orpressurized dispenser for metering out the contents, having a labeldescribing it, in substance, as a toothpaste, gel or dental cream.

Organic surface-active agents are used in the compositions of thepresent invention to achieve increases prophylactic action, assist inachieving thorough and complete dispersion of the anticalculus agentthroughout the oral cavity, and render the instant compositions morecosmetically acceptable. The organic surface-active material ispreferably anionic, nonionic or ampholytic in nature, and it ispreferred to employ as the surface-active agent a detersive materialwhich imparts to the composition detersive and foaming properties.Suitable examples of anionic surfacants are water-soluble salts ofhigher fatty acid monoglyceride monosulfates, such as the sodium salt ofthe monosulfated monoglyceride of hydrogenated coconut oil fatty acids,higher alkyl sulfates such as sodium lauryl sulfate, alkyl arylsulfonates such as sodium dodecyl benzene sulfonate, higher alkylsulfoacetates, higher fatty acid esters of 1,2 dihydroxy propanesulfonate, and the substantially saturated higher aliphatic acyl amidesof lower aliphatic amino carboxylic acid compounds, such as those having12 to 16 carbons in the fatty acid, alkyl or acyl radicals, and thelike. Examples of the last mentioned amides are N-lauroyl sarcosine, andthe sodium, potassium, and ethanolamine salts of N-lauroyl, N-myristoyl,or N-palmitoyl sarcosine which should be substantially free from soap orsimilar higher fatty acid material. The use of these sarcosinatecompounds in the oral compositions of the present invention isparticularly advantageous since these materials exhibit a prolonged andmarked effort in the inhibition of acid formation in the oral cavity dueto carbohydrate breakdown in addition to exerting some reduction in thesolubility of tooth enamel in acid solutions.

Examples of water-soluble nonionic surfactants are condensation productsof ethylene oxide with various reactive hydrogen-containing compoundsreactive therewith having long hydrophobic chains (e.g. aliphatic chainsof about 12 to 20 carbon atoms), which condensation products("ethoxamers") contain hydrophilic polyoxyethylene moieties, such ascondensation products of poly(ethylene oxide) with fatty acids, fattyalcohols, fatty amides, polyhydric alcohols (e.g. sorbitan monostearate)and polypropyleneoxide (e.g. Pluronic materials).

Various other materials may be incoporated in the oral preparations ofthis invention such as whitening agents, preservatives, silicones,chlorophyll compounds, other anticalculus agents, and/or ammoniatedmaterial such as urea, diammonium phosphate, and mixtures thereof. Theadjuvants, where present, are incorporated in the preparations inamounts which do not significantly adversely affect the properties andcharacteristics desired.

Any suitable flavoring or sweetening material may also be employed.Examples of suitable flavoring constituents are flavoring oils, e.g. oilof spearmint, peppermint, wintergreen, sassafras, clove, sage,eucalyptus, majaram, cinnamon, lemon, and orange, and methyl salicylate.Suitable sweetening agents include sucrose, lactose, maltose, sorbitol,xylitol, sodium cyclamate, perillartine, APM (aspartyl phenyl alanine,methyl ester), saccharine and the like. Suitably, flavor and sweeteningagents may together comprise from about 0.1% to 5% more of thepreparation.

In the preferred practice of this invention, these dentifricecompositions are preferably applied to dental surface, e.g. toothenamel, preferably by brushing, regularly such as 1 to 3 times daily,followed preferably by rinsing the oral cavity.

The following Examples A-F illustrate the preparation of operativesynthetic cross-linked polymers and their properties. All parts, amountsand proportions referred to herein and in the appended claims are byweight, and temperatures are in degrees C unless otherwise indicated.

    ______________________________________                                        Post Polymerization Cross-Linking                                                         Example A  Example B                                              ______________________________________                                        PVM/MA*       0.33330 Moles                                                                              0.33001 Moles                                      PEG 600**     0.00166 Moles                                                                              0.00249 Moles                                      MEK***        6.6          6.6                                                ______________________________________                                         *Gantrez AN139, vinylmethyl ether/maleic anhydride 1/1 copolymer M.W.         500,000 (GAF Corp.).                                                          **Polyethylene glycol, M.W 600 (13-14 E.O.)                                   ***Methyl ethyl ketone                                                   

The PVM/MA copolymer is dissolved in the MEK (b.pt. 80° C.) yielding a10 wt. % solution, in a stirred 1 liter resin kettle. The PEG is thenadded and the liquor refluxed for about 4 hours. At least 400 ml. of MEKare collected by distillation through a cold water condenser. A pinkviscous syrup results which is poured at 50°-60° C. into a largeevaporating dish and further devolatized under vacuum at 60°-70° C.overnight.

Though the starting PVM/MA copolymer is both ketone-soluble andwater-soluble to a high degree, the products of both Examples 1 and 2are pink, very hard solids, only slightly soluble in ketones, andinsoluble but rapidly swelling in water to form gels. I.R. spectrumanalyses show that the starting polymer has no free --COOH groups butboth products show strong-COOH peaks resulting from ring opening andester cross-links, indicative of an Example A product containing about0.5 mole % or about 2 wt. % of PEG cross-linkages and an Example Bproduct containing about 0.75 mole % or about 3 wt. % of PEGcross-linkages.

Concurrent Cross-Linking Polymerization EXAMPLE C

In a one liter pressure reactor are charged the following: 404.4 partscyclohexane, 269.6 parts ethyl acetate, and 6 parts 1,7 octadiene. 0.3Parts of the initiator t-butylperoxypavilate are added at 58° C. inthree increments of 0.1 part each at times: 0, 60, and 120 minutes fromthe first addition. Seventy-five parts of molten maleic anhydride and49.0 parts of methyl vinyl ether are mixed together and gradually addedto the reaction vessel at 58° C. and 65 psi (natural pressure of thesystem) over a 2 hour period of time. The reaction mixture is then heldat 58° C. for two hours after the last addition of initiator. Thepresence of maleic anhydride is followed by testing with triphenylphosphene. The product precipitates out of solution (slurrypolymerization). After the reaction is complete, the product is cooledto room temperature, filtered and dried in a vacuum oven. It is a 1:1cross-linked copolymer of methyl vinyl ether and maleic anhydride(PVM/MA) containing about 4.6 wt. % of the octadiene cross-linkingagent.

EXAMPLE D

The procedure of Example C is repeated using 5 parts of 1,9-decadieneinstead of the 6 parts of 1,7-octadiene. The product, in the form of awhite powder, has the following viscosity specifications in varyingconcentrations in aqueous solution at pH 7 and 25° C. by Brookfield RVT,Spindle TC at 10 RPM:

                  TABLE 1                                                         ______________________________________                                        Concentration   Viscosity                                                     ______________________________________                                        0.25%           30,800 cps                                                    0.50%           63,500 cps                                                    1.00%           90,000 cps                                                    ______________________________________                                    

An 0.5% aqueous solution of this product, Ph adjusted to 7 has thefollowing viscosity properties when measured with a Brookfield ModelRVT, Spindle TC, at varying RPM's:

                  TABLE 2                                                         ______________________________________                                               RPM   Viscosity                                                        ______________________________________                                               1     376 × 10.sup.3                                                    2.5   180 × 10.sup.3                                                    5     105 × 10.sup.3                                                    10     59 × 10.sup.3                                             ______________________________________                                    

These results show that even at very low concentrations thiscross-linked PVM/MA copolymer yields highly viscous solutions.

The following yield points of varying concentrations of this polymer inaqueous solution at pH 7 are obtained using the Haake RotoviscometerRV12 with MV IP sensor system and shear rates varied from 0 to 10 sec⁻¹:

                  TABLE 3                                                         ______________________________________                                        Concentration Yield Point (Pascals)                                           ______________________________________                                        0.125         37                                                              0.250         64                                                              0.500         180                                                             ______________________________________                                    

These high-yield points, corresponding to the amount of shear stressneeded to initiate flow, indicate gel network formation enablingpermanent stabilization of suspensions of particles such as insolublepolishing materials in dentifrice compositions.

EXAMPLE E

One percent aqueous solutions of cross-linked PVM/MA copolymercontaining from 0.01% to 10% of 1,7-octadiene cross-linking agent,prepared as described in Example C, are shaken overnight in order tohydrolyze the maleic anhydride ring and then neutralized with NaOH tofully ionize the carboxyl groups. The results listed in the followingtable indicate that solutions containing more than 2.5%, i.e. at leastabout 3% of cross-linking agent gel whereas solutions containing up to2.5% cross-linking agent do not gel.

                  TABLE 4                                                         ______________________________________                                        Wt. % Cross-Linking Agent                                                                        Gelling Result                                             ______________________________________                                        0.1                No gel                                                     0.5                "                                                          1.0                "                                                          2.5                "                                                          5.0                Gelled                                                     7.5                "                                                          10.0               "                                                          ______________________________________                                    

EXAMPLE F Optional Hydrolysis Procedure

To a 2 liter kettle fitted with a mechanical agitator and a refluxcolumn add 962 grams of deionized water and 28 grams of a 10% aqueoussodium hydroxide solution. Heat to 65° C. and add 10 grams of theproduct of Example D with stirring. The system becomes clear within 2hours and has a pH of about 7. The resultant gel has a solids content of1%.

The following examples are only illustrative of the dentifricecompositions of this invention. Typically, the cross-linked polymer orcopolymer is hydrolyzed in water or water/humectant mixtures with asufficient amount of base to neutralize the acid preferably attemperatures ranging from 40°-60° C. The resulting dispersion is mixedwith the other dentifrice ingredients at a pH of about 7.

    ______________________________________                                        Opacified Dental Gel Formulations                                                         Weight Percent                                                    Example       1       2         3     4                                       ______________________________________                                        XL Polymer A* 0.5     --        --    --                                      XL Polymer B**                                                                              --      0.5       0.7   --                                      XL Polymer C***                                                                             --      --        --    1.3                                     Glycerine     25.0    --        25.0  25.0                                    Polyethylene  3.0     --        3.0   3.0                                     Glycol 600                                                                    Sorbitol      31.7    62.8      34.8  35.2                                    (70% Aqueous                                                                  Solution)                                                                     Sodium Hydro- 0.20    0.40      0.40  0.50                                    xide (50%)                                                                    NaF           0.242   0.242     0.242 0.242                                   Tetrasodium   0.50    0.50      0.50  0.50                                    Pyrophosphate                                                                 Na Saccharin  0.20    0.20      0.20  0.20                                    TiO.sub.2     0.30    0.30      0.30  0.30                                    Na Benzoate   0.50    0.50      0.50  0.50                                    Zeodent 113   18.0    23.0      23.0  23.0                                    (SiO.sub.2)                                                                   Sylodent 700  5.5     --        --    --                                      (SiO.sub.2)                                                                   Flavor        0.89    0.89      0.89  0.89                                    Sodium Lauryl 1.20    1.20      1.20  1.20                                    Sulfate (SLS)                                                                 Water, q.s. to                                                                              100     100       100   100                                     ______________________________________                                        Dental Cream Formulations                                                                Weight Percent                                                     Example      5           6       7                                            ______________________________________                                        XL Polymer B 0.75        1.0     0.25                                         Carboxymethyl                                                                              --          1.3     0.5                                          Cellulose (CMC)                                                               Glycerine    19.9        10.2    25.0                                         Polyethylene 3.0         3.0     3.0                                          Glycol 600                                                                    Sorbitol     33.8        22.5    35.0                                         (70% Aqueous                                                                  Solution)                                                                     NaOH (50%)   0.3         --      0.3                                          Tetrasodium  0.5         1.5     0.5                                          Pyrophosphate                                                                 Tetrapotassium                                                                             --          4.5     --                                           Pyrophosphate                                                                 Na Saccharin 0.2         0.4     0.2                                          TiO.sub.2    0.3         --      0.3                                          FD&C Blue #1 --          0.4     --                                           Zeodent 113  25.0        23.0    25.0                                         (SiO.sub.2 )                                                                  Flavor       0.89        0.95    0.89                                         Sodium Lauryl                                                                              1.2         1.2     1.2                                          Sulfate                                                                       Water, q.s. to                                                                             100         100     100                                          ______________________________________                                        Opacified Dental Gel Formulations                                                        Weight Percent                                                     Example      8          9       Control A                                     ______________________________________                                        Glycerine    25.0       25.0    25.0                                          Sorbitol     36.2       36.2    38.1                                          (70% Aqueous                                                                  Solution)                                                                     Polyethylene 3.0        3.0     3.0                                           Glycol 600                                                                    Carboxymethyl                                                                              0.5        --      0.4                                           Cellulose (CMC)                                                               Xanthan Gum  --         0.4     --                                            X1 Polymer B 0.3        0.3     --                                            Tetrasodium  0.5        0.5     0.5                                           Pyrophosphate                                                                 Saccharin    0.2        0.2     0.2                                           NaF          0.243      0.243   0.243                                         TiO.sub.2    0.3        0.3     0.5                                           Flavor       0.89       0.89    0.89                                          Silica Thickener                                                                           --         --      5.5                                           (Sylodent 15)                                                                 Silica Abrasive                                                                            20.0       20.0    18.0                                          (Zeodent 113)                                                                 Sodium Lauryl                                                                              1.2        1.2     1.2                                           Sulfate (SLS)                                                                 Water, q.s. to                                                                             100        100     100                                           ______________________________________                                         *Cross-linked PVM/MA of Example A containing about 0.5 mole % of PEG 600      crosslinking agent                                                            **Crosslinked PVM/MA of Example C containing about 5 wt. % of 1,7octadien     crosslinking agent                                                            ***Crosslinked PVM/MA of Example E containing about 10% of 1,7octadiene       crosslinking agent                                                       

Viscosity Profiles

Brookfield viscosities of the formulations of Examples 8, 9 and Controlare measured as a function of time following the SPI No. 7707-1procedure using Brookfield RVTD, spindle T-E, at 5 RPM, with thefollowing results:

    ______________________________________                                                              Brookfield Units                                                                        3    30   90                                  Formulation                                                                            % XL Polymer B                                                                             % Gum     Days Days Days                                ______________________________________                                        Example 8                                                                              0.3          0.5 CMC   23.5 25.0 28.5                                Example 9                                                                              0.3          0.4 Xanthan                                                                             20.0 21.0 22.5                                Control A                                                                              --           0.4 CMC   29.0 38.0 41.5                                ______________________________________                                    

The above results indicate substantially less progressive thickeningwith cross-linked polymer-containing formulations compared to a controlcontaining CMC and silica thickener.

Stress Growth Test to Determine Dispensibility

Stress growth measurements to determine dispensibility of the dentifriceare performed using Rheometrics System Four instrument at constant shearrate of 10 sec⁻¹ and as function of time, with the following results.

    ______________________________________                                        Formulation   Stress (Dynes/cm.sup.2)                                         ______________________________________                                        Example 8     7,500                                                           Example 9     6,000                                                           Control A     9,500                                                           ______________________________________                                    

The highest shear stress produced is indicative of the amount of workrequired to dispense the dentifrice. The above results indicate thatcross-linked polymer-containing formulations are substantially easier todispense than the control.

This invention has been described with respect to certain preferredembodiments and it will be understood that modifications and variationsthereof obvious to those skilled in the art are to be included withinthe spirit and purview of this application and the scope of the appendedclaims.

We claim:
 1. A linear viscoelastic dentifrice composition in the form ofa toothpaste or dental gel with a pH of about 4 to about 9 comprising anorally acceptable water/humectant vehicle, an orally acceptable dentalpolishing agent and, in an amount effective to render the compositionlinearly viscoelastic, a synthetic linearly viscoelastic cross-linkedpolymeric thickening agent derived from a polymer containing repeatingunits in which one or more phosphonic acid groups are bonded to one ormore carbon atoms in the polymer chain and having in a 1 wt. % aqueoussolution an elastic or storage modulus G" and a viscous or loss modulusG" substantially independent of frequency in an applied frequency rangeof 0.1 to 100 radians/sec, a G' minimum value of 1,000 dynes/sq.cm whichvaries less than 1 order of magnitude of its original value, and a ratioof G"/G' ranging from more than 0.05 to less than
 1. 2. A compositionaccording to claim 1 containing approximately by weight, 6% to 50% ofwater, 20to 70% of humectant, 5 to 70% of dental polishing agent, and0.02% to 5% of said polymeric thickening agent containing at least about3% of cross-linking agent.
 3. A composition according to claim 1 whereinthe said polymeric thickening agent is made with a cross-linking agentcontaining at least two ethylenically unsaturated groups or at least twogroups reactive with pendant reactive groups along the polymer chain ofthe polymeric thickening agent.
 4. A composition according to claim 3wherein said thickening agent is made with 1,7-octadiene, 1,9-decadiene,or polyethylene glycol as cross-linking agent.
 5. A compositionaccording to claim 4 wherein said polymeric thickening agent comprisesunits of styrene phosphonic acid, vinyl phosphonic acid and/or vinylphosphonyl fluoride.
 6. A composition according to claim 1 wherein thepolymeric thickening agent has a molecular weight of about 1,000 toabout 5,000,000 and comprises units of styrene phosphonic acid, vinylphosphonic acid and/or vinyl phosphonyl fluoride.
 7. A compositionaccording to any one of claims 1, 2, 3, 4 or 5 wherein the polymericthickening agent has a molecular weight of about 1,000 to about5,000,000.
 8. A composition according to any one of claims 1, 2, 3, 4 or5 further containing an amount of a fluoride ion source sufficient tosupply about 25 ppm to about 5,000 ppm of fluoride ions.
 9. Acomposition according to claim 6 further containing an amount of afluoride ion source sufficient to supply about 25 ppm to about 5,000 ppmof fluoride ions.
 10. A composition according to claim 8 furthercontaining about 0.4 to about 3 parts of xanthan gum or carboxymethylcellulose per part of the cross-linked polymeric thickening agent.
 11. Acomposition according to claim 9 further containing about 0.4 to about 3parts of xanthan gum or carboxymethyl cellulose per part of thecross-linked polymeric thickening agent.
 12. A method of promoting oralhygiene comprising applying to dental surface an effective amount of acomposition as defined in any one of claims 1, 2, 4-6, 9 or
 11. 13. Amethod of promoting oral hygiene comprising applying to dental surfacean effective amount of a composition as defined in claim
 8. 14. A methodof promoting oral hygiene comprising applying to dental surface aneffective amount of a composition as defined in claim 10.